Connecting a power source, such as a radio frequency ("RF") power source, to a device, such as an RF match unit, can be hazardous if the connecting cable can be disengaged at the device while still attached, at the other end, to the power source, resulting in an open live cable end. To avoid this hazard, the cable may be configured so as not to provide a disconnection at the device, thus allowing the connecting cable to be disengaged at the power source. However, in industrial applications, cables are commonly not supplied with equipment. Rather, the equipment includes standard connection jacks for receipt of industry standard cables.
One known solution to having a live open end on a connecting cable typically involves an interlocked switch provided between the cable and device. The interlocked switch disables a power source when the connecting cable is disengaged at the device. Interlocked switches typically include two bulky housings which enclose a male/female connection and a microswitch that is actuated by mating the housings around the male/female connection. The microswitch is in turn connected by a control wire to control circuits that switch the power source off when the male/female connection is disengaged. Unfortunately, some of the interlocked switches rely heavily on the integrity of equipment operators since the housings can be mated and activate a power source without enclosing the male/female connection. The incentive to bypass an interlocked switch arises when the interlocked components are time consuming to use properly.
FIG. 1 (Prior Art) shows such an interlocked switch assembly for disabling an A/C power source 10 which powers a semiconductor processing platform 12 which typically includes two or more high vacuum chambers 14, 16. Each chamber 14, 16 typically receives RF power through an RF match unit 18, 20 from an RF source 22, 24 which employs A/C power. The RF sources 22, 24 are connected to the RF match units 18, 20 by flexible RF cables 26, 28 having male connectors on each end. Connection of each RF cable 26, 28 at the RF match unit 18, 20 presents the possibility of a dangling live male connector. Each chamber 14, 16 typically has an independently powered interlock circuit 30, 31 which is disabled by an interlock switch string 32, 33 unless an interlocked switch 34, 36 is closed to establish a completed male/female RF connection at the RF match unit 18, 20.
FIG. 2 (Prior Art) shows an interlocked switch 34 positioned to be closed after a male RF connector 42 on the RF cable 26 and a female RF connector 44 on the RF match unit 18 are mated to supply RF power to the RF match unit. The interlocked switch 34 is closed by joining a first housing 46 and a second housing 48 around the RF connection.
FIG. 3 (Prior Art) is a schematic circuit diagram for the interlocked switch assembly of FIG. 1. The independently powered interlock circuit 30 includes a battery 50, a contactor 52 which interrupts power to the chamber 14 from the A/C power source 10, and a relay 54 which is closed by a current in the interlock switch string 32. The interlock switch string 32 includes the relay 54 and further includes a separate power source 56, the interlocked switch 34 which interlocks the RF match unit 18, and one or more additional switches 58, 59 which interlock other components with the A/C power source 10 to the chamber 14.
There is a need for a passive interlocked switch for use with connecting cables which connect a device to a power source wherein the interlocked switch does not require separate action by an operator to connect or disconnect the interlocked switch when replacing the connecting cable. It would be desirable if the interlocked switch was not easily bypassed.